Srimad Bhagavatam Canto 10, Chapter 78, Text 17

SB 10.78.17

srutva yuddhodyamam ramah
 kurunam saha pandavaih
tirthabhiseka-vyajena
 madhya-sthah prayayau kila
 
Translation: 
 
Lord Balarama then heard that the Kurus were preparing for war with the Pandavas. Being neutral, He departed on the pretext of going to bathe in holy places.
 
Purport: 
 
Both Duryodhana and Yudhisthira were dear to Lord Balarama, and so to avoid an awkward situation He departed. Furthermore, after killing the demon Viduratha, Lord Krsna put aside His weapons, but Lord Balarama still had to kill Romaharsana and Balvala to finish relieving the earth of her burden of demons.
Srimad Bhagavatam Canto 10, Chapter 78, Text 16
Srimad Bhagavatam Canto 10, Chapter 78, Text 18